1. Field of the Invention
The present invention relates to keypads, and more particularly to a keypad structure for inputting signals into electronic devices including but not limited to those having vibration motors.
2. Background of the Related Art
FIG. 1 shows a folding-type mobile communication terminal of the related art. This terminal includes an upper part 1 and a lower part 2. A lower end of the upper part is hinge-coupled with an upper end of the lower part so as to turn within a predetermined range of angles. The terminal also includes a speakerphone 4 and a liquid crystal display screen 5 which displays characters and numbers. These elements are installed on a front part of a case of the upper part. Also included is a keypad 7 and side buttons 8. The keypad has a plurality of key buttons 10 formed thereon and is installed on a front part of a case 6 of the lower folding portion. The side buttons control the volume of the speakerphone and are installed at one lateral side of the case.
As shown in the enlarged view of FIG. 2, the keypad is mounted inside the case so that tops of key buttons 10 protrude out of the case through corresponding key button holes 9 formed on the front part of the case. Also, the side buttons are inserted through corresponding side button holes 11, so that top and bottom portions of the corresponding side buttons protrude from the side of the case.
The side buttons operate by activating a tact switch 12. As shown, a nose 13 of the tact switch contacts the bottom portion of the side button protruding inward into the case so as to support the side button 8. At another end, the tact switch is attached to a printed-circuit board 14 installed inside the case, so as to adhere closely to a rear face of the keypad. In operation, pressure is applied to nose 13 of the tact switch when a user presses a side button. A tact switch signal is then transferred to the printed-circuit board 14 in order to adjust the volume of the speaker phone.
This related-art terminal has a number of drawbacks. For example, a stroke of the nose of the tact switch is usually only 0.2 mm. If an assembly tolerance is +0.2 mm at a place where the side button is coupled with the case, then when the terminal is assembled the side button may push against a predetermined portion of the tact switch. As a result, the on/off operation of the tact switch 12 may be lost or at least adversely affected.
In order to overcome such a disadvantage, it has been proposed to couple the assembly of the side button with the case in such a maimer that one face of the keypad is just in contact with the nose of the tact switch. While this approach may have some limited success, it is complicated to perform and thus significantly increases the assembly time of the terminal.
FIG. 3 shows an enlarged cross-sectional view of the mobile terminal of FIG. 2. In this view, side button 8 and tact switch 12 are coupled with case 6 and printed-circuit board 14 (not shown in this figure) so as to maintain an interval of 0.1 mm between the nose of the tact switch and the adjacent bottom of the side button.
This modification of the related art also has drawbacks. In this arrangement, the side button is not fixed to the side button hole 11, but rather is merely inserted into the side button hole for assembly. As a result, the side button may float and thus may be affected by a vibration motor which is activated in the terminal when a call is received. More specifically, the side button may collide with the nose of the tact switch when the variation motor is activated, thereby producing an undesirable noise. Moreover, if the interval between the bottom 15 of the side button and the nose 13 of the tact switch becomes greater than −0.2 mm by the assembly tolerance, the tact switch may fail to smoothly operate when the side button is pushed.
A need therefore exists for a terminal which demonstrates improved resistance to vibration compared with related-art terminals, while at the same time prevents malfunctions from occurring as a result of inaccurate assembly tolerances relating to one or more function keys on the terminal.